Certain 2-(2-substituted benzoyl)-1,3-cyclohexanedione herbicides are described in U.S. patent application Ser. Nos. 532,869, filed Sept. 16, 1983; 587,331, filed Mar. 7, 1984; 634,408, filed July 31, 1984; 532,882, filed Sept. 16, 1983; 566,077, filed Dec. 27, 1982; and 640,791, filed Aug. 17, 1984 and are incorporated herein by reference.
The herbicidal compounds can have the following structural formula ##STR2## wherein R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are hydrogen or C.sub.1 -C.sub.4 alkyl; R.sup.6 is chlorine, C.sub.1 -C.sub.4 alkoxy or C.sub.1 -C.sub.4 alkythio; and R.sup.7 is C.sub.1 -C.sub.4 alkyl; and n is the integer 0 or 2.
These herbicides can be prepared by reacting a dione of the structural formula ##STR3## wherein R, R.sup.1, R.sup.2, R.sup.3, R.sup.4 and R.sup.5 are as defined with a mole of trisubstituted benzoyl cyanides of the structural formula ##STR4## wherein R.sup.6 and R.sup.7 are as defined above.
A slight mole excess of zinc chloride (ZnCl.sub.2) is used in a suitable solvent such as methylene chloride along with the two reactants. A slight mole excess of triethylamine is slowly added to the reaction mixture with cooling. The resulting mixture is stirred at room temperature for several hours and the reaction product is worked up by conventional techniques.
The trisubstituted benzoyl cyanides can be prepared from their corresponding tri-substituted benzoyl chlorides which are preparable from their corresponding tri-substituted benzoic acids, according to processes described in detail hereinafter.